The present invention relates to machines for processing stacks of paper sheets or the like, especially to bookbinding machines of the type wherein the backs of stacked signatures are coated with films of adhesive and the adhesive is thereupon caused to set prior to attachment of book covers.
The backs of stacks of paper sheets in a bookbinding machine are normally provided with adhesive during transport between the jaws of suitable holders which form part of an endless conveyor. If the adhesive is a thermosetting adhesive (e.g., a starch-containing wet glue), the stacks are transported through a drying station which is located downstream of the adhesive-applying station and wherein the adhesive is heated (and its setting promoted) by flames which are obtained as a result of combustion of a gaseous fuel. The heating action of gas flames must be regulated with a high degree of accuracy because the safety factor which is prescribed by authorities is extremely high, i.e., the gas flames are very small and their heating and drying action is limited so that the heating station occupies an inordinately large amount of space, especially if the thermosetting adhesive is used in a high-speed bookbinding machine. Therefore, the heating of thermosetting adhesive with gas flames contributes excessively to the bulk, especially length, of a high-speed bookbinding or analogous machine.